Poppet valves are used to control the flow of fluids and as such have been proven to offer a robust method of controlling and sealing fluids that are aggressive, for example where the fluids have high temperatures and pressures. In particular, poppet valves usually operated by rotating cams operating to overcome springs which act in a manner to close the valves have been employed to control the flow of air or air and fuel mixtures into, and the exit of the products of combustion from, the combustion chambers of internal combustion engines.
By careful selection of the cam profile, it is possible to make small changes to the manner in which the valve closure approaches the valve seat and the manner and rate at which the closure moves between closed and open positions, and vice versa, quite apart from the times for which the valve is actually open and closed. This pattern of movement of the closure will be referred to as the valve movement profile.
Where the cams are rotated by the engine, it is in general impossible to alter the valve movement profile as between one engine speed or loading and another. However it has been long recognised that greater efficiency can be achieved if a different valve movement profile is employed at different speeds or loadings. But where mechanically driven cams are concerned with fixed cam profiles, the latter have to be selected to give the best compromise valve movement profile over the expected range of engine speeds and loadings.
It is common practice to define the cam profile in order to ensure that the landing speed of the valve closure is a small fraction of the maximum velocity of the valve, in order to reduce impact stress on the valve seating on closure, while providing a high speed movement of the valve closure on opening and at other parts of its travel.
When running an engine at high speed there is a need to operate poppet valves with high levels of acceleration and deceleration, and it is often found that the forces generated by push-rods, cams or springs are a limiting factor on the speed at which an engine can be run.
In an attempt to better control the opening and closing of inlet and exhaust valves of an internal combustion engine and in particular vary the valve movement profile at different operating speeds, it has already been proposed to replace the cams by electromagnetic solenoid actuators driven by electric current from a computer controlled engine management system. But hitherto the results have been less than satisfactory. Thus, when used to open and close such valves at high speeds, solenoid actuators have been found to produce high landing speeds and the control systems cannot regulate the kinetic energy of the valves as operating speeds increase. Furthermore, electromagnetic solenoid actuation does not achieve speeds of valve operation required of inlet and exhaust valves of the combustion chambers containing the pistons of an internal combustion engine designed to run at high speeds.
It is an object of the present invention to provide a magnetic actuator better suited to control the opening and closing of the inlet and exhaust valves of an internal combustion engine.
It is also an object of the invention to provide a power supply for operating the actuator in an energy efficient manner.